On a map drawn three-dimensionally, symbols which represent landforms such as mountains, vehicles and the like are drawn with polygonal map constituents such as polygons. A navigation device uses a display method of displaying a polygon (hereinafter, referred to as an “own-vehicle polygon” in some case), which represents a vehicle (hereinafter, referred to as an “own vehicle” in some case) on which the same device is mounted, in a mode of looking down from a viewpoint located at a high position rear of the own-vehicle polygon.
In this display method, there is a problem that the own-vehicle polygon is hidden by a polygon (hereinafter, referred to as a “landform polygon” in some case), which represents a landform higher than the position of the viewpoint, for example, a mountain, when the own vehicle passes through a tunnel or the like, which is formed in the mountain.
Technologies for avoiding the problem in the prior art are disclosed, for example, in Patent Documents 1 to 5. For example, in a technology disclosed in Patent Document 1, the problem in the prior art is avoided by using means for setting an altitude of the viewpoint to a place higher than an altitude of such a constituent of the map.